1. Field of the Invention
The present invention relates to a semiconductor device having high performance and high reliability, in which an electronic component is mounted on a substrate by using an adhesive (for example, by flip chip mounting), and the occurrence of gas bubbles inside the adhesive is reduced, and also relates to a method for manufacturing such a semiconductor device at low cost and with high efficiency.
2. Description of the Related Art
Conventionally, flip chip mounting is used as a method for mounting electronic components on a substrate, since the manufacturing process is straightforward, and allows rapid and inexpensive mounting. As a flip chip mounting method, for example, there is known a method in which an adhesive is supplied previously onto a substrate, an electronic component (for example, a semiconductor chip) formed with bumps composed of metal, or the like, on electrode pads is placed opposing the substrate, a load is applied to the semiconductor chip, and the adhesive is cured, thereby connecting (mounting) the semiconductor chip on the substrate (see Japanese Patent Application Laid-Open (JP-A) Nos. 60-262430 and 09-97816). Furthermore, a suitable adhesive is a thermoplastic insulating resin, such as an epoxy resin, for example, since it can be cured in a short period of time.
In the flip chip mounting described above, a heated semiconductor chip is pressed against the adhesive by heating the semiconductor chip to a prescribed temperature while applying pressure. In so doing, the adhesive is heated rapidly, the viscosity thereof falls and the fluidity increases, and therefore the adhesive is pushed so as to extend over the whole surface of the semiconductor chip. Furthermore, during this, thermal curing proceeds simultaneously and the adhesive becomes cured. Due to the adhesive force of the cured adhesive and the curing and contracting action, the bumps formed on the electrode pads of the semiconductor chip become connected to the bonding terminals formed on the substrate, while being maintained in a state of pressurized contact with these bonding terminals.
However, in flip chip mounting of this type, there is a problem in that gas bubbles occur inside the cured adhesive. If the adhesive contains gas bubbles, then due to the moisture content inside the gas bubbles, when the semiconductor device is mounted on a motherboard, or the like, by reflow soldering, then swelling or delamination, or the like, occurs in the adhesive due to the explosion of the water vapor, and this may lead to connection faults in the bump junction sections, or the like. Furthermore, if gas bubbles are present in the vicinity of the bump junctions, then due to the effects of the moisture and impurity ions in the bubbles, and the like, electric current leakage arises between mutually adjacent bumps, leading to degradation of the properties of the semiconductor device or to malfunction of the device, and hence the presence of gas bubbles inside the adhesive has a detrimental effect on the reliability of the semiconductor device.
Possible reasons for the occurrence of gas bubbles include, for example: the incorporation of air bubbles into the adhesive when the adhesive is applied to the substrate, the generation of gas bubbles due to gas arising from the adhesive or the substrate (for example, a resin substrate) during heating, or the incorporation of air bubbles into the adhesive during the flowing movement of the adhesive when it is pushed and spread. These gas bubbles often occur in the vicinity of the interface with the substrate, and since the substrate has undulations in the interface with the adhesive, particularly in the wiring sections (interconnection sections) and the bonding terminal sections on the substrate, then the gas bubbles are liable to enter into these undulations during the flowing movement and curing of the adhesive.
It is possible to use an adhesive in any form, such as a film or a paste, but an adhesive in the form of a film has virtually no fluidity and therefore when the adhesive is attached to a substrate, a large number of bubbles may be incorporated at the interface with the substrate where undulations are present, and hence gas bubbles are more liable to occur in the vicinity of the interface with the substrate, in comparison with an adhesive in the form of a paste.
In recent years, in accordance with increasing integration of semiconductor chips, the pitch between bumps has become extremely fine, the size of bumps has become smaller and the height of bumps has become lower. Furthermore, in response to the increasingly fine bump pitch, the bonding terminals and wires on the substrate have also become increasing fine. Therefore, the undulations present at the interface between the adhesive and the substrate have become finer, and in the flip chip mounting method described above, gas bubbles become more liable to enter into these finer undulations. As the bump pitch becomes finer and the bump height becomes lower in this way, then the gap between the semiconductor chip and the substrate after flip chip mounting becomes smaller and the thickness of the adhesive layer becomes thinner. Therefore, the relative size of the gas bubbles with respect to this thickness increases and gas bubbles of a size which are not problematic conventionally give rise to the problems described above.
As a method for resolving the problem of the generation of air bubbles, a flip chip connection method has been proposed which includes, for example, a first step of applying an adhesive made of a thermally curable resin onto the surface of a wiring substrate, a second step of holding a bare chip with a heating tool, mutually aligning the positions of the bumps on the bare chip and the pads on the wiring substrate by placing the element forming surface of the bare chip toward the surface of the wiring substrate, and heating the bare chip via the heating tool, and a third step of abutting the bumps against the pads and curing same, by pressurizing the heated bare chip toward the wiring substrate (see Japanese Patent Application Laid-Open (JP-A) No. 2001-244298). In this case, before applying pressure, the heating tool which lies in contact with the adhesive is heated, thereby causing the adhesive to flow, whereupon pressurization is started, and furthermore, since the heating tool is heated in a stepwise fashion during each flip chip mounting operation, then it is difficult to shorten the mounting time. Furthermore, if bonding is repeated in a continuous operation, then time is required to allow the heating tool to cool after each flip chip mounting operation, and therefore reduction of the mounting time is also difficult for this reason. Consequently, there is a problem in that the productivity is low and cost reductions cannot be achieved.
Furthermore, as a method for manufacturing a semiconductor component in which a flip chip is mounted on a substrate circuit, a method has been proposed in which, firstly, a liquid resin layer having a convex spherical upper surface is formed to a planar shape corresponding to the flip chip, on the substrate circuit, by using a stencil printing unit in vacuum conditions, whereupon the flip chip is aligned in position and mounted on the resin layer, and the flip chip is then pressure bonded while heating, onto the substrate circuit (see Japanese Patent Application Laid-Open (JP-A) No. 2000-100870). In this case, since the application of an adhesive is performed by stencil printing in a vacuum, then when the members are introduced into the vacuum chamber and removed from the vacuum chamber, time is required to reduce the atmosphere to a vacuum and then return the atmosphere to normal pressure, and hence there is a problem of low productivity. Furthermore, since manufacturing equipment provided with a vacuum chamber is required, then this gives rise to higher costs. Moreover, with stencil printing, it is difficult to control the supply of an adhesive in very small quantities, and therefore it is not possible to respond to very small gaps or very fine pitches. Furthermore, a printing mask which corresponds to the size of the chip being mounted is required, and therefore it is difficult to achieve a low-cost operation.
Moreover, there has also been a proposal of a semiconductor device having a flip chip structure in which a semiconductor chip, and a circuit substrate having electrodes at positions opposing electrodes on a surface opposing the semiconductor chip, are connected electrically via a connecting resin, by means of a flip chip technique, wherein through holes, which are situated to the outer side of the outer circumference of the semiconductor chip and at least partially situated inside the region where the circuit substrate is covered with the connecting resin, are provided in the circuit substrate (see Japanese Patent Application Laid-Open (JP-A) No. 2001-127194). The through holes in the semiconductor device are provided to form channels for the purpose of facilitating the removal of humidity from the region of gas bubbles, rather than suppressing the actual occurrence of gas bubbles, and in addition to restricting the freedom of design of the substrate, forming such through holes may also obstruct the formation of fine wiring and give rise to increase in the substrate manufacturing costs and increase in the size of the semiconductor device.
Consequently, at present, a semiconductor device having high performance and high reliability, in which the occurrence of gas bubbles inside the adhesive when mounting an electronic component onto a substrate by using an adhesive (for example, flip chip mounting) is reduced, and a method for manufacturing such a semiconductor device at low cost and with high efficiency, have not yet been proposed, and the development of technology capable of reducing the occurrence of gas bubbles inside the adhesive is sought, particularly in cases where the bump pitch is very fine.